1. Field of the Invention
The present invention relates to a surge detection device applicable to centrifugal and mixed flow pumps, blowers, and compressors, and relates also to a turbomachine having variable guide vanes and the surge detection device
2. Description of the Related Art
When a centrifugal or mixed flow pump is operated below the design flow rate of the pump, flow separation occurs in the impeller and diffuser and other components in the pump, and the flow undergoes a periodic pressure fluctuation. This leads to a phenomenon called "surge" which causes the system as a whole to begin self-induced vibration, thereby disabling pump operation. To avoid the onset of surge, this phenomenon must be detected early in the operation of the pump, and some remedial steps must be taken to prevent surge from occurring.
Conventionally, surge condition of the pump is judged by monitoring some operating parameters such as pressure, flow rate, temperature and time-averaged operating parameters, and comparing the monitored results with previously-determined values of the parameters to determine whether the system is surging or operating normally.
In the prior art, surge is determined by detecting a rapidly rising temperature in the following techniques disclosed in: a Japanese Patent Application (JPA), Second Publication, H5-53956, a JPA, First Publication, S62-113889, a JPA, First Publication, S59-77089, a JPA, First Publication, S59-79097, a JPA, First Publication, S56-2496, for example. An increase in pressure is used as a surge signal in the techniques disclosed in a JPA, First Publication, S63-161362; a JPA, First Publication, S58-57098; and a JPA, First Publication, S55-114896, for example. Surge is detected as a pressure difference between a hub and a shroud of a diffuser in a JPA, First Publication, H3-199700; as a pressure difference between a pressure surface and a suction surface of the diffuser vane, in a JPA, First Publication, S62-51794; and from the pressure waveforms in a JPA, First Publication, S63-94098, for example
Other techniques utilize: the rate of change of lift as a measure of the efficiency of the blades as disclosed in a JPA, First Publication, S57-129297; or the differentials of the axial vibrations in a JPA, First Publication, H4-47197; or detection of vibrations with a microphone as disclosed in a JPA, First Publication, H3-213696, for example
All such conventional techniques are based an indirect approach of comparing a pre-determined value of some time-averaged operating parameters, such as pressure and temperature, with the current operating parameters for the determination of the surge state of a system. Therefore, a quick and accurate determination of surge is difficult with these conventional techniques, because the problem in the existing techniques is that even though pre-testing runs are performed to determine the surge condition of a test system, it is not possible to determine the surge condition of another actual system accurately, because the onset of surge depends on the capacity of the piping in the operating system. Furthermore, because the detection is based on time-averaging of operating parameters, detection lags the onset of surge, and therefore, the response action is delayed, and for such reasons, the existing devices are of limited practical use.
The present invention is presented to solve the problems in the existing surge detection devices and turbomachine based on the existing techniques of surge detection, and an objective is to present a surge detection device which is capable of detecting surge condition rapidly and accurately in a turbomachine operating at a flow rate less than the design flow rate, and to present a turbomachinery which can be operated even at low flow rates by providing a rapid and accurate indication of surge based on the surge detection device of the present invention.